1. Field of the Invention
The present invention relates generally to electrocardiographic apparatus, and, more particularly, to a method and apparatus for selecting a sensor pair forming a lead from a multi-sensor electrocardiogram sensor set to be a physiologically standardized lead to monitor the electrocardiographic performance of an individual.
2. Description of the Prior Art
A fundamental tool used to monitor and diagnose cardiovascular functioning of an individual is the electrocardiogram. An electrocardiogram is the plot of the waveform created by electrical signals generated by the cardiac functioning of an individual. The signals are actually indications of depolarization and repolarization of cardiac tissue. These electrical signals are detected by electrical contact sensors placed on the individual, and the signals detected by the sensors are plotted. The resultant waveforms are then analyzed in order to evaluate the cardiovascular performance of the individual.
Typically, ten electrocardiogram sensors are positioned at different locations on the individual with the specific locations being selected for geometric considerations. Several of the sensors are bipolar which are placed on the arms and legs (i.e., the extremities) of the individual, and the remaining sensors are unipolar and are placed on the chest area of the individual. The unipolar sensors are referenced with respect to intercoastal space, a midclavicular line, an anterior axillary line, and a midaxillary line. In these positions, the bipolar and unipolar sensors are referred to as being in a geometrically standardized placement.
A significant problem inherent in the use of electrocardiograms is that the resulting waveforms are position determinative, that is to say, the signals sensed by a sensor are dependent on where the sensor is positioned on the individual's body.
In fact, this variance is the reason why a plurality of sensors (i.e., ten for a standard twelve lead electrocardiogram) are utilized. By increasing the number of sensors, the chances that a medically significant signal might be missed is reduced. However, a diagnosis based upon a reduced chance of missing a medically significant signal is still ambiguous, and may place a patient at risk.
It is therefore a customary practice to employ average values derived by calculating average values of all the waveforms obtained from all of the sensors. However, this practice results in a diagnosis being made based upon average values; such a diagnosis may still be ambiguous or inaccurate.
It is therefore an object of the present invention to provide a method and apparatus for selecting an electrode sensor pair to be a physiologically standardized electrode pair from the multi-sensor electrocardiogram electrode sensor set from which analysis of the cardiac functioning of an individual may be performed. Accordingly, a physiologically standardized electrode sensor pair is defined as that pair which generates the largest waveform component, i e., the largest R-wave amplitude, T-wave amplitude, P-wave amplitude, Q-wave amplitude, or S-wave amplitude.
It is a further object of the present invention to provide a set of electrocardiogram sensors positioned in a preconstructed unit such that the sensors are maintained at defined distances from one another to allow a sensor pair to be selected from the set to be utilized as a physiologically standardized electrode pair.
For example, depolarization is the physiological principle for the creation of the R-wave component and repolarization is the physiological principle for the T-wave component of an electrocardiogram . By placing electrode sensor pairs in a physiologically standardized manner on two or more subjects the maximum component waveforms R and T for all subjects can then be measured and compared. As a corollary, the underlying physiological principles for the creation of the component waveforms can be compared and diagnostically analyzed. It is therefore a further object of this invention to provide physiologically standardized electrode sensor pairs for diagnostic analysis of physiological phenomena responsible for the creation of waveform components of an electrocardiogram. Geometrically standardized electrode sensor pairs do not permit such a comparison of the physiological phenomena.